The present invention relates to a lead frame for a semiconductor device mounting a semiconductor chip such as a semiconductor integrated circuit chip and a transistor, a method of manufacturing the lead frame, a semiconductor device and a method of manufacturing the semiconductor device. More particularly, it relates to improvement in reliability and application to multi-pin devices.
A conventional lead frame will be described with reference to drawings.
FIG. 27 is a plan view for showing the structure of the conventional lead frame. As is shown in FIG. 27, the conventional lead frame includes a rectangular outer frame 110; a rectangular die pad 101 disposed at substantially the center of an area surrounded with the outer frame 110 for mounting a semiconductor chip; first inner leads 102, second inner leads 103, third inner leads 104 and fourth inner leads 105 electrically connected with the semiconductor chip mounted on the die pad 101 through connecting means such as metal wires; first outer leads 106, second outer leads 107, third outer leads 108 and fourth outer leads 109 respectively formed continuous with the first inner leads 102, the second inner leads 103, the third inner leads 104 and the fourth inner leads 105 for connection with external terminals; a dam bar 111 for connecting and fixing the first outer leads 106, the second outer leads 107, the third outer leads 108 and the fourth outer leads 109; and tie-bars 113 for connecting the corners of the outer frame 110 with the corresponding corners of the die pad 101. In this manner, the die pad 101 is supported by the tie-bars 113 in the conventional lead frame.
The conventional lead frame is manufactured through procedures as is shown in FIGS. 28(a) and 28(b). FIGS. 28(a) and 28(b) are partial plan views for showing the manufacturing procedures for the conventional lead frame, wherein merely the upper right portion of the lead frame is shown.
First, as is shown in FIG. 28(a), a metal plate 114 is etched or pressed, thereby forming, in the metal plate 114, the die pad 101, the tie-bars 113, the inner leads 102 through 105 (among which the inner leads 103 and 104 are not shown) connected with the die pad 101, the outer leads 106 through 109 (among which the outer leads 107 and 108 are not shown) formed continuous with the inner leads 102 through 105 for connection with external terminals, the outer frame 110, and the dam bar 111 for connecting and fixing the outer leads 106 through 109. Thus, a lead frame body 115 is formed. At this point, every two inner leads are connected with each other at their tips among the inner leads 102 through 105.
Then, as is shown in FIG. 28(b), the tips of the inner leads 102 through 105 of the frame body 115 are cut off (a tip cutting procedure), so that the inner leads 102 through 105 can be separated from the die pad 101 and independent of one another. After the procedure shown in FIG. 28(a) and before the procedure shown in FIG. 28(b), a plating procedure for plating the lead frame body 115 can be carried out. In the procedure shown in FIG. 28(b), since every two inner leads are connected with each other among the inner leads 102 through 105 in the previous procedure, the connected tips are cut off.
Next, a semiconductor device using the conventional lead frame will be described. FIG. 29 is a plan view of a conventional semiconductor device, and FIG. 30 is a sectional view taken on line XXX--XXX of FIG. 29.
As is shown in FIGS. 29 and 30, a semiconductor chip 116 is bonded onto the die pad 101 supported by the tie-bars 113, and the first inner leads 102, the second inner leads 103, the third inner leads 104 and the fourth inner leads 105 are disposed in the vicinity of respective sides of the semiconductor chip 116, namely, a first side 116a, a second side 116b, a third side 116c and a fourth side 116d, respectively. Electrode pads 117 of the semiconductor chip 116 are electrically connected with the inner leads 102, 103, 104 and 105 through metal wires 118. Then, the semiconductor chip 116, the die pad 101, the tie-bars 113, the inner leads 102, 103, 104 and 105 and the metal wires 118 are sealed with a sealing resin 119, so that the first outer leads 106, the second outer leads 107, the third outer leads 108 and the fourth outer leads 109 can be protruded from the sealing resin 119. Ultimately, the dam bar 111 is cut off, the outer frame 110 is removed, and the outer leads 106, 107, 108 and 109 are formed into desired shapes. Thus, the semiconductor device is completed.
In the plan view of FIG. 29, the sealing resin 119 is shown as a transparent substance, and merely the outline thereof is shown.
However, the conventional lead frame and the conventional semiconductor device using the lead frame have the following problems:
First, when the lead frame is used for a semiconductor device, the outer leads are protruded from the side faces of the semiconductor device as external terminals. Therefore, there is a limit in compactness in the packaging area.
Second, even when the inner leads and the outer leads are formed with small pitches therebetween and a semiconductor chip having a large number of electrode pads is mounted, there is a limit in application to multi-pin devices. Actually, the applicable number of pins is limited to approximately 160.
Third, since the lead frame includes the dam bar, the procedure for cutting off the dam bar and forming the outer leads into desired shapes is indispensable after the resin sealing procedure in the manufacture of a semiconductor device. Therefore, there is also a limit in decreasing the manufacturing procedures for the semiconductor device.